Dielectric porcelain composition and dielectric resonator using the composition

ABSTRACT

A dielectric porcelain composition includes MgTiO 3  and Mg 2 SiO 4  and satisfies a+b=1 and 0&lt;b&lt;1, wherein a denotes a molar ratio of MgTiO 3  and b denotes a molar ratio of Mg 2 SiO 4 . It can include MgTiO 3  and CaTiO 3  and satisfy a+c=1 and 0&lt;c≦0.15, wherein a has the same meaning as shown above and c denotes a molar ratio of CaTiO 3 . It can also include MgTiO 3 , Mg 2 SiO 4  and CaTiO 3  and satisfy a+b+c=1, 0&lt;b&lt;1 and 0&lt;c≦0.15, wherein a, b and c have the same meanings as shown above. These compositions can be manufactured, with the content of Mg 2 SiO 4 , the content of CatiO 3  and the contents of Mg 2 SiO 4  and CaTiO 3  adjusted, respectively. These compositions can be used as dielectric materials to manufacture dielectric resonators.

The present invention relates to a dielectric porcelain compositionparticularly excellent in characteristics at a millimeter-wave bandwidthregion, a dielectric resonator using the composition, and a process forthe manufacture of the composition and resonator capable of controllingthe characteristics (relative permittivity εr and temperaturecoefficient τf).

DESCRIPTION OF THE PRIOR ART

While various dielectric materials have been known as dielectricmaterials for high frequency, magnesium titanate-based dielectricmaterials have been known as one of the materials having a relativelyhigh Qf value. According to “Ceramics Engineering Handbook,” edited byJapan Ceramics Society and published by Gihodo, Vol. 1, p. 1885, May 30,1993, MgTiO₃ that is a magnesium titanate-based dielectric material, hasrelative permittivity εr of 17, a Qf value of 110000 GHz and temperaturedependency of resonance frequency (temperature coefficient τf) of −45ppm/K.

In addition, improvements in magnesium titanate-based materials havealso been proposed. For example, JP-B SHO 61-14605 discloses adielectric material obtained by sintering a material containing titaniumdioxide and more than 1 mole and not more than 1.3 moles of magnesiumoxide per mole of the titanium dioxide. As the characteristics of thedielectric material of the prior art, it is disclosed that the relativepermittivity εr=17.3 and no load Qu=12000 (120000 GHz in terms of the Qfvalue) when MgO:TiO₂=1.2:1.

JP-A 2002-193662 discloses dielectric porcelain comprising a firstcrystal phase of at least one species consisting of MgTiO₃, CaTiO₃,Mg₂SiO₄ and BaTi₄O₉, a second crystal phase of at least one speciesconsisting of Mg₂TiO₄, Mg₂B₂O₅ and Li₂TiSiO₅ and oxides of Si, B and Li,with the aim of materializing dielectric porcelain having a high Qfvalue, with neither flexion nor distortion produced when being calcinedtogether with a conductive material.

Though the technologies in the field of date communications haverecently been developed conspicuously, the characteristics required fordielectric materials used for dielectric resonators or other suchdevices, including the aforementioned Qf value, tend to be diversifieddue to applications, frequency bandwidths and the like.

In consideration of an application particularly as a resonator material,it is required from a standpoint of ready design to develop dielectricmaterials having relative permittivity εr low to a certain extent as oneof the characteristics of dielectric materials for submillimeter-waveand millimeter-wave regions. Since the dimension of a resonancephenomenon is directly proportionate to ε^(−1/2) when the dielectricconstant is defined as ε, when a material having high relativepermittivity is used, the dimension of a resonator has to be extremelysmall with an increasing frequency. In order to make it easy to design aresonator, it is demanded to develop a dielectric material havingappropriate relative permittivity εr taking the entire dimension andworkability into consideration.

When the dielectric material is used for a resonator, it is generallynoted that the temperature coefficient τf is desirably as small aspossible. It is further preferable in view of the temperaturecoefficient of the peripheral parts and other such surrounding partsthat the temperature coefficient be set at an optional value to acertain extent.

From these viewpoints, the prior art technologies, such as thosedisclosed by JP-B SHO 61-14605 and JP-A 2002-193662, for example, payprincipal attention to an improvement in the Qf value and Q value, withrelative permittivity εr and temperature coefficient τf taken littleinto consideration.

In the materials available on the market, which have small relativepermittivity εr and small temperature coefficient τf, the former isabout 12.6 and the latter is about −10 ppm/K. These values do notnecessarily suffice.

The present invention has been proposed in view of the state of theconventional affairs.

One object of the present invention is to provide a dielectric porcelaincomposition and a dielectric resonator using the composition, in whichthe relative permittivity εr can be adjusted to a relatively smallvalue, and it is made possible to readily design submillimiter-waveresonators and millimeter-wave resonators, for example.

Another object of the present invention is to provide a dielectricporcelain composition and a dielectric resonator using the composition,in which the temperature coefficient τf can be made small as much aspossible and slightly adjusted in accordance with the surroundingcircumstances and the like.

Still another object of the present invention is to provide a dielectricporcelain composition and a dielectric resonator using the composition,in which the relative permittivity εr has been adjusted to a small valueto a certain extent and the temperature coefficient τf has been adjustedto the vicinity of zero.

Yet another object of the present invention is to provide a process foroptionally adjusting the characteristics (relative permittivity εr andtemperature coefficient τf) of a dielectric porcelain composition.

The present inventors have keenly continued their studies over a longperiod of time in order to attain the objects mentioned above. As aresult, they have found that addition of Mg₂SiO₄ to MgTiO₃ enables therelative permittivity εr to be freely adjusted in accordance with thecontent of Mg₂SiO₄, with the temperature coefficient τf varied little,and also to be set optimum in submillimeter-wave or millimeter-wavebandwidth regions and that addition of CaTiO₃ to MgTiO₃ enables thetemperature coefficient τf to be set optional in the vicinity of zero inaccordance with the content of CaTiO₃, with the relative permittivity εrnot so much varied. The present invention has been perfected based onthese findings.

According to one aspect of the present invention, a dielectric porcelaincomposition comprising MgTiO₃ and Mg₂SiO₄ is characterised in that thecomposition satisfies a+b=1 and 0<b<1, wherein a denotes a molar ratioof MgTiO₃ and b denotes a molar ratio of Mg₂SiO₄; a dielectric porcelaincomposition comprising MgTiO₃ and CaTiO₃ is characterised in that thecomposition satisfies a+c=1 and 0<c≦0.15, wherein a denotes a molarratio MgTiO₃ of and c denotes a molar ratio of CaTiO₃; or a dielectricporcelain composition comprising MgTiO₃, Mg₂SiO₄ and CaTiO₃ ischaracterised in that the composition satisfies a+b+c=1, 0<b<1 and0<c≦0.15, wherein a denotes a molar ratio of MgTiO₃, b denotes a molarratio of Mg₂SiO₄ and c denotes a molar ratio of CaTiO₃.

In the dielectric porcelain compositions, relative permittivity εr andtemperature coefficient τf can be obtained at optional values,respectively, in the range of 6.8 to 18 and in the range of −55 to +55ppm/K. There can be realized a dielectric porcelain composition havingrelative permittivity εr in the vicinity of 10 and temperaturecoefficient τf in the vicinity of zero, for example.

The dielectric porcelain composition can be used as a dielectricmaterial for dielectric resonators, such as submillimeter-waveresonators and millimeter-wave resonators. Therefore, the dielectricresonator of the present invention uses the dielectric porcelaincomposition as its resonator material.

As described above, the addition of Mg₂SiO₄ to MgTiO₃ enables therelative permittivity εr to be freely adjusted in accordance with thecontent of Mg₂SiO₄, and the addition of CaTiO₃ to MgTiO₃ enables thetemperature coefficient τf to be set optional in the vicinity of zero inaccordance with the content of CaTiO₃. In view of these, the adjustmentof the contents of these components enables adjustment of thecharacteristics of a dielectric porcelain composition to be obtained.

According to another aspect of the present invention, there is provideda manufacturing process for the dielectric porcelain composition, whichcan control the characteristics of the composition. Specifically, thecontents of Mg₂SiO₄ and CaTiO₃ are adjusted respectively withinpredetermined ranges to adjust the relative permittivity εr andtemperature coefficient τf.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, characteristic features and advantages ofthe present invention will become apparent to those skilled in the artfrom the description to be give herein below with reference to theaccompanying drawings, in which:

FIG. 1 is a flow chart showing one example of a manufacturing processfor a dielectric porcelain composition according to the presentinvention,

FIG. 2 is an X-ray diffraction chart of 0.6MgTiO₃-0.4Mg₂SiO₄,

FIG. 3 is a characteristic diagram showing the relationship betweenMg₂SiO₄ content and the relative permittivity εr in a system ofMgTiO₃—Mg₂SiO₄,

FIG. 4 is a characteristic diagram showing the relationship betweenMg₂SiO₄ content and the temperature coefficient τf in the MgTiO₃—Mg₂SiO₄system,

FIG. 5 is a characteristic diagram showing the relationship between thecalcining temperature and the relative density in the MgTiO₃—Mg₂SiO₄system,

FIG. 6 is an X-ray diffraction chart of 0.91MgTiO₃-0.09CaTiO₃,

FIG. 7 is a characteristic diagram showing the relationship betweenCaTiO₃ content and the relative permittivity εr in a system ofMgTiO₃—CaTiO₃,

FIG. 8 is a characteristic diagram showing the relationship betweenCaTiO₃ content and the temperature coefficient τf in the MgTiO₃—CaTiO₃system,

FIG. 9 is a characteristic diagram showing the relationship between thecalcining temperature and the relative density in the MgTiO₃—CaTiO₃system,

FIG. 10 is an X-ray diffraction chart of0.2275MgTiO₃-0.6825Mg₂SiO₄-0.09CaTiO₃,

FIG. 11 is a characteristic diagram showing the results of relativepermittivity εr measured in a system of MgTiO₃—Mg₂SiO₄—CaTiO₃, with 0.05mol of CaTiO₃ fixed and with the Mg₂SiO₄ substitution amount varied,

FIG. 12 is a characteristic diagram showing the results of temperaturecoefficient τf measured in the MgTiO₃—Mg₂SiO₄—CaTiO₃ system, with 0.05mol of CaTiO₃ fixed and with the Mg₂SiO₄ substitution amount varied,

FIG. 13 is a characteristic diagram showing the results of relativedensity measured in the MgTiO₃—Mg₂SiO₄—CaTiO₃ system, with 0.05 mol ofCaTiO₃ fixed and with the Mg₂SiO₄ substitution amount varied,

FIG. 14 is a characteristic diagram showing the results of relativepermittivity εr measured in a system of MgTiO₃—Mg₂SiO₄—CaTiO₃, withMgTiO₃:Mg₂SiO₄ fixed to 1:3 and with the CaTiO₃ substitution amountvaried,

FIG. 15 is a characteristic diagram showing the results of temperaturecoefficient τf measured in the MgTiO₃—Mg₂SiO₄—CaTiO₃ system, withMgTiO₃:Mg₂SiO₄ fixed to 1:3 and with the CaTiO₃ substitution amountvaried, and

FIG. 16 is a characteristic diagram showing the results of relativedensity measured in the MgTiO₃—Mg₂SiO₄—CaTiO₃ system, withMgTiO₃:Mg₂SiO₄ fixed to 1:3 and with the CaTiO₃ substitution amountvaried.

The dielectric porcelain composition, dielectric resonator using thecomposition and manufacturing process for the composition according tothe present invention will be described hereinafter in detail.

The dielectric porcelain composition of the present invention comprisesmagnesium titanate MaTiO₃ added with either one or both of Mg₂SiO₄ andCaTiO₃.

Though MaTiO₃ has excellent characteristics that include a high Qfvalue, it exhibits slightly high relative permittivity εr of about 18.2and large temperature coefficient τf of −57 ppm/K. In view of this,added to MaTiO₃ in the present invention are Mg₂SiO₄ to improve therelative permittivity εr and CaTiO₃ to improve the temperaturecoefficient τf.

When Mg₂SiO₄ is added to MaTiO₃, the relative permittivity εr decreasessubstantially in proportion to the content of Mg₂SiO₄, whereas thetemperature coefficient τf varies little. On the other hand, when CaTiO₃is added to MaTiO₃, the temperature coefficient τf shifts gradually fromthe minus side to the plus side, whereas the relative permittivity εrarises little. For these reasons, the relative permittivity εr andtemperature coefficient τf can independently be controlled depending onthe contents of Mg₂SiO₄ and CaTiO₃.

From these standpoints, Mg₂SiO₄ or CaTiO₃ is added to MaTiO₃. It ispreferable that the content of Mg₂SiO₄ should satisfy that a+b=1 andthat 0<b<1, wherein a denotes the molar ratio of MgTiO₃ and b denotesthe molar ratio of Mg₂SiO₄. Controlling the content of Mg₂SiO₄optionally to satisfy these enables the relative permittivity εr to befreely controlled to a value lower than that MaTiO₃ has, e.g. in therange of 6.8 to 18. However, when the relative permittivity εr is to beset at a value suitable for use in submillimeter-wave andmillimeter-wave regions, e.g. a value of not more than 12, the b is morepreferably defined as 0.5≦b<1.

In the case of CaTiO₃ added to MaTiO₃, it is preferable that the contentthereof should satisfy that a+c=1 and that 0<c≦0.15, wherein a denotes amolar ratio of MgTiO₃ and c denotes a molar ratio of CaTiO₃. Controllingthe content of CaTiO₃ optionally to satisfy these enables thetemperature coefficient τf to be freely controlled to a value in therange of −55 to +55 ppm/K. In order to control the temperaturecoefficient τf to be as close as zero, i.e. around 30 ppm/K, however,the c is more preferably defined as 0.03≦c≦0.08.

When both Mg₂SiO₄ and CaTiO₃ are added to MaTiO₃, the contents thereofmay be adjusted to respectively suitable amounts to satisfy thata+b+c=1, that 0<b<1 and that 0<c≦0.15, wherein a denotes a molar ratioof MgTiO₃, b denotes a molar ratio of Mg₂SiO₄ and c denotes a molarratio of CaTiO₃.

In order to control the relative permittivity εr to be a value suitablefor use in submillimeter-wave and millimeter-wave regions, e.g. a valueof not more than 12, and the temperature coefficient τf to be as closeas zero, the contents of Mg₂SiO₄ and CaTiO₃ may be adjusted as mentionedabove. Though their respective optimum values are slightly differentfrom the defined values, the more preferably ranges are 0.5≦b<1 and0.05≦c≦0.09, respectively.

It is noted that since it is clear from the X-ray diffraction that therespective components of the dielectric porcelain composition existrespectively in the form of MgTiO₃, Mg₂SiO₄ and CatiO₃ and that thematrix thereof is a crystal phase having the three components combined,the composition is to be represented by their ratios in mol.

Based on the above, by controlling the ratios of the respectivecomponents, a dielectric porcelain composition exhibiting the relativepermittivity εr of 10.86, temperature coefficient τf of −2.7 ppm/K andQf value of 74000 GHz can be materialised.

The manufacturing process for the dielectric porcelain compositionaccording to the present invention will be described herein below. Theflow chart thereof adopted by the present invention is as shown in FIG.1.

In the manufacturing process of the present invention, MgO, TiO₂, CaCO₃and SiO₂ are used as raw materials, for example. While the respectivecomponents are mixed in accordance with their respectively desiredcharacteristics, since the prepared composition is reflectedsubstantially as it is by the composition of the dielectric porcelaincomposition, the raw material components are mixed so that the preparedcomposition and the composition of the dielectric porcelain compositioncan have the relationship of 1:1.

The process of manufacturing the dielectric porcelain composition willbe described. The raw materials, MgO, TiO₂, CaCO₃ and SiO₂, are mixed ata mixing process 1 to obtain a mixture. The mixture is subjected to adrying process 2 and a shaping process 3 and preliminarily calcined at acalcining process 4. The preliminary calcining is performed in order forthe reaction of the raw materials to proceed to a certain extent andgenerally at a temperature slightly lower than that used in thesintering.

The preliminarily calcined product is milled at a milling process 5 andthen dried at a drying process 6. The dried product is granulated at agranulating process 7. In the granulating process, a binder is mingledwith the dried product. Though any optional binder can be used,polyvinyl alcohol or the like can advantageously be used, for example.

The granulated product is shaped into a desired shape at a shapingprocess 8 and sintered at a sintering process 9. The sinteringtemperature used at the sintering process is adjusted in the range of1250° C. to 1500° C., for example. The optimum sintering temperature ismade slightly different depending on the raw materials for thedielectric porcelain composition. When manufacturing a dielectricporcelain composition comprising MgTiO₃ and Mg₂SiO₄, the sinteringtemperature of not less than 1300° C. is preferred. In this case, whenthe sintering temperature is less than 1300° C., the Qf value will belowered and the relative density will also be lowered. In the case of adielectric porcelain composition comprising MgTiO₃ and CaTiO₃, it ispreferable to use the sintering temperature of not less than 1250° C.When it is less than 1250° C., both the Qf value and the relativedensity are lowered similarly to the case mentioned above. When adielectric porcelain composition comprising MgTiO₃, Mg₂SiO₄ and CaTiO₃is to be manufactured, the sintering temperature of not less than 1300°C. is preferable. By setting the sintering temperature within theaforementioned range, the Qf value and relative density can bemaintained at high levels, respectively.

In the manufacturing process, MgO, TiO₂, CaCO₃ and SiO₂ are used as theraw materials. However, this is by no means limitative. For example,MgTiO₃, Mg₂SiO₄ and CaTiO₃ can be prepared in advance at theirpredetermined ratios and used in the manufacturing process.

The dielectric porcelain composition can be used at the frequencybandwidths of submillimeter-waves and millimeter-waves, e.g. 30 to 300GHz. The frequency bandwidths include that of a radar for automobiles(using the frequency of 77 GHz:38.5 GHz multiplied by 2).

Therefore, the dielectric porcelain composition of the present inventioncan be used as a material for resonators used in the submillimeter-waveand millimeter-wave regions and a substrate material for MICdielectrics, and for dielectric waveguides, dielectric antennas,impedance matching of various kinds of millimeter-wave circuits andother such electronic parts. It can suitably be used for dielectricresonators.

The present invention will be described based on concrete experimentalresults.

Samples of a dielectric porcelain composition were produced inaccordance with the following procedure.

MgO, TiO₂, CaCO₃ and SiO₂ were weighed so that these raw materials had apredetermined mixing ratio and then mixed with a ball mill for 16 hours.The mixture obtained was dried at 120° C. for 24 hours and then shapedunder a shaping pressure of 200 kgf/cm² into a disc 60 mm in diameter.

The disc was preliminarily calcined at 1100° C. for 2 hours, then milledfor 16 hours using the ball mill and dried at 120° C. for 24 hours. Thedried product was granulated, with 1% by weight of polyvinyl alcoholadded thereto, and shaped under a shaping pressure of 2000 kgf/cm² intoa 12 mm-diameter.

Finally, the shaped product was principally calcined to obtaindielectric porcelain composition samples.

In accordance with the process of producing the dielectric porcelaincomposition samples, MgTiO₃ and Mg₂SiO₄ used as raw materials were mixedso that b is in the range of 0 to 1, provided that a+b=1, when the molarratio of MgTiO₃ was defined as a and the molar ratio of Mg₂SiO₄ wasdefined as b. The mixture was sintered at a temperature of 1250° C. to1500° C. to obtain various samples.

A sample of 0.6MgTiO₃-0.4Mg₂SiO₄, wherein a=0.6 and b=0.4, was measuredusing an X-ray diffraction apparatus. The results of measurement areshown in FIG. 2. It can be observed from the X-ray diffraction chartthat there exist peaks resulting respectively from MgTiO₃ and Mg₂SiO₄,from which it is found that the sample comprises a mixed crystal ofMgTiO₃ and Mg₂SiO₄.

The relative permittivity εr and temperature coefficient τf of eachsample were measured in accordance with the “Method of TestingDielectric Characteristics of Fine Ceramics for Microwaves” of theJapanese Industrial Standards (JIS R 1627). The results of relativepermittivity εr measurement are shown in FIG. 3 and Table 1 below, andthe results of temperature coefficient τf measurement are shown in FIG.4 and Table 2 below.

TABLE 1 Molar ratio Relative Relative Relative Relative Relative b ofpermittivity permittivity permittivity permittivity permittivity Mg₂SiO₄εr at 1300° C. εr at 1350° C. εr at 1400° C. εr at 1450° C. εr at 1500°C. 0.0 17.90 18.16 18.24 18.17 18.22 0.1 16.05 16.33 16.36 16.24 16.070.2 14.06 14.61 14.67 14.64 14.41 0.4 11.23 11.88 11.99 11.93 11.84 0.510.25 10.53 10.64 10.63 10.62 0.6 9.54 9.59 9.65 9.67 9.69 0.8 7.93 7.998.08 8.14 8.16 0.9 7.26 7.41 7.45 7.47 7.49 1.0 6.55 6.89 6.98 6.99 6.91

TABLE 2 Molar ratio b Temperature coefficient of Mg₂SiO₄ τf at 1450° C.(ppm/K) 0.0 −57.6 0.1 −52.1 0.2 −58.0 0.4 −60.3 0.5 −62.1 0.6 −62.8 0.8−63.1 0.9 −64.0 1.0 −65.3

As is clear from FIG. 3 and Table 1 above, it is found that the relativepermittivity εr gradually decreases in proportion as the Mg₂SiO₄ contentincreases. As shown in FIG. 4 and Table 2 above, it is found that thetemperature coefficient τf varies little even when the Mg₂SiO₄ contentvaries.

This means that controlling the Mg₂SiO₄ content enables the relativepermittivity εr to be controlled without affecting the othercharacteristic (temperature coefficient τf). Particularly when the molarratio b of Mg₂SiO₄ is set to be 0.5 or more, the relative permittivityεr of 12 or less can be materialised.

The relative density of each sample produced was also measured. Theresults of measurement are shown in FIG. 5 and Table 3 below. As isclear from FIG. 5 and Table 3, while the relative density shows a slightdrop at 1300° C., it varies little at a temperature of more than 1300°C. Desired relative density could not be obtained when the calciningtemperature was 1200° C. or less (not shown). Therefore, when Mg₂SiO₄ isused to control the relative permittivity εr, it can be said that thecalcining temperature is preferably set to be 1300° C. or more.

TABLE 3 Relative Relative Relative Relative Relative Molar densitydensity density density density ratio b of (%) at (%) at (%) at (%) at(%) at Mg₂SiO₄ 1300° C. 1350° C. 1400° C. 1450° C. 1500° C. 0.0 97.598.4 99.0 98.7 98.6 0.1 97.6 98.6 98.6 98.0 97.6 0.2 95.5 97.7 98.2 97.897.1 0.4 93.5 96.9 97.4 97.3 96.8 0.5 92.9 96.3 97.9 97.2 97.1 0.6 92.595.6 98.2 97.0 96.9 0.8 91.5 94.8 97.6 97.0 96.9 0.9 90.9 94.0 97.6 96.997.8 1.0 90.2 92.3 97.8 97.1 97.5

In accordance with the process of producing the dielectric porcelaincomposition samples, MgTiO₃ and CaTiO₃ used as raw materials were mixedso that c is in the range of 0 to 0.09, provided that a+c=1, when themolar ratio of MgTiO₃ was defined as a and the molar ratio of CaTiO₃ wasdefined as c. The mixture was principally calcined at a temperature of1300° C. to obtain various samples.

In FIG. 6, shown are measurement results of a sample of0.91MgTiO₃-0.09CaTiO₃, wherein a=0.91 and c=0.09, measured using anX-ray diffraction apparatus. It can be observed from the X-raydiffraction chart that there exist peaks resulting respectively fromMgTiO₃ and CaTiO₃, from which it is found that the sample comprises amixed crystal of MgTiO₃ and CaTiO₃.

The relative permittivity εr and temperature coefficient τf of eachsample were measured in accordance with the “Method of TestingDielectric Characteristics of Fine Ceramics for Microwaves” of theJapanese Industrial Standards (JIS R 1627). The results of relativepermittivity εr measurement are shown in FIG. 7 and Table 4 below, andthe results of temperature coefficient τf measurement are shown in FIG.8 and Table 5 below.

TABLE 4 Relative Relative Relative Relative Relative Molar ratiopermittivity permittivity permittivity permittivity permittivity c ofCaTiO₃ εr at 1250° C. εr at 1300° C. εr at 1350° C. εr at 1400° C. εr at1450° C. 0.00 17.80 17.90 18.16 18.24 18.17 0.05 19.80 19.94 20.08 20.5120.47 0.07 21.22 21.45 21.70 21.98 22.02 0.09 22.82 22.98 23.27 23.5223.41

TABLE 5 Molar ratio c Temperature coefficient of CaTiO₃ τf at 1300° C.(ppm/K) 0.00 −57.6 0.05 −8.6 0.07 18.7 0.09 48.3

As is clear from FIG. 8 and Table 5 above, it is found that thetemperature coefficient τf gradually varies in proportion as the CaTiO₃content increases. When the molar ratio c of CaTiO₃ is around 0.06, thetemperature coefficient τf becomes substantially zero, and shifts to theminus side when the ratio is smaller than 0.06 and to the plus side whenthe ratio is larger than 006. On the other hand, the relativepermittivity εr does not vary so much even when the CaTiO₃ contentvaries, as shown in FIG. 7 and Table 4 above. This means thatcontrolling the CaTiO₃ content enables the temperature coefficient if tobe independently controlled. Particularly when the molar ratio c ofCaTiO₃ is set to be in the range of 0.03 to 0.08, the temperaturecoefficient τf can be controlled in the range of ±30 ppm/K.

The relative density of each sample produced was also measured. Theresults of measurement are shown in FIG. 9 and Table 6 below. As isclear from FIG. 9 and Table 6, the relative density shows a level notgiving rise to any problem when the temperature is 1250° C. or more.Therefore, when CaTiO₃ is used to control the temperature coefficientτf, it can be said that the calcining temperature is preferably set tobe 1250° C. or more.

TABLE 6 Relative Relative Relative Relative Relative density densitydensity density density Molar ratio (%) at (%) at (%) at (%) at (%) at cof CaTiO₃ 1250° C. 1300° C. 1350° C. 1400° C. 1450° C. 0.00 97.0 97.598.4 99.0 98.7 0.05 95.6 96.4 96.8 98.1 98.2 0.07 96.2 96.8 97.7 98.899.1 0.09 96.8 97.9 98.3 99.2 99.1

In accordance with the process of producing the dielectric porcelaincomposition samples, samples each comprising MgTiO₃, Mg₂SiO₄ and CaTiO₃were produced.

FIG. 10 shows measurement results of a sample of0.2275MgTiO₃-0.6825Mg₂SiO₄-0.09CaTiO₃, wherein a=0.2275, b=0.6825 andc=0.09, measured using an X-ray diffraction apparatus. It can beobserved from the X-ray diffraction chart that there exist peaksresulting respectively from MgTiO₃, Mg₂SiO₄ and CaTiO₃, from which it isfound that the sample comprises a mixed crystal of MgTiO₃, Mg₂SiO₄ andCaTiO₃.

In a system of MgTiO₃—Mg₂SiO₄—CaTiO₃, various samples were prepared,with 0.05 mol of CaTiO₃ fixed (c=0.05) and with the Mg₂SiO₄ substitutionamount varied. In this case, the results of relative permittivity εrmeasured are shown in FIG. 11 and Table 7 below, the results oftemperature coefficient τf measured in FIG. 12 and Table 8 below, andthe relative density measured in FIG. 13 and Table 9 below.

TABLE 7 Molar Relative Relative Relative ratio b permittivity εr atpermittivity εr at permittivity εr at of Mg₂SiO₄ 1300° C. 1350° C. 1400°C. 0.0000 19.94 20.08 20.51 0.2375 15.41 15.24 14.57 0.4750 11.85 11.3111.25 0.7125 9.46 9.42 9.43 0.9500 7.60 7.83 7.48

TABLE 8 Molar ratio b Temperature coefficient of Mg₂SiO₄ τf at 1300° C.(ppm/K) 0.0000 −8.6 0.2375 −21.1 0.4750 −30.5 0.7125 −40.6 0.9500 −44.7

TABLE 9 Molar ratio b Relative density Relative density Relative densityof Mg₂SiO₄ (%) at 1300° C. (%) at 1350° C. (%) at 1400° C. 0.0000 96.496.8 98.1 0.2375 96.9 96.7 94.7 0.4750 96.2 93.8 92.3 0.7125 97.1 96.095.9 0.9500 96.1 98.3 96.5

In the MgTiO₃—Mg₂SiO₄—CaTiO₃ system, various samples were produced, withMgTiO₃:Mg₂SiO₄ fixed to 1:3 and with the CaTiO₃ substitution amountvaried. In this case, the results of relative permittivity εr measuredare shown in FIG. 14 and Table 10 below, the results of temperaturecoefficient τf measured in FIG. 15 and Table 11 below, and the relativedensity measured in FIG. 16 and Table 12 below.

TABLE 10 Relative Relative Relative Molar ratio c permittivity εr atpermittivity εr at permittivity εr at of CaTiO₃ 1300° C. 1350° C. 1400°C. 0.00 8.43 8.45 0.05 9.46 9.42 9.43 0.07 10.01 9.91 9.95 0.09 10.7010.86 10.84

TABLE 11 Molar ratio c Temperature coefficient of CaTiO₃ τf at 1350° C.(ppm/K) 0.00 −62.0 0.05 −40.6 0.07 −27.3 0.09 −2.9

TABLE 12 Molar ratio c Relative density Relative density Relativedensity of CaTiO₃ (%) at 1300° C. (%) at 1350° C. (%) at 1400° C. 0.0095.8 96.7 0.05 97.1 96.0 95.9 0.07 96.5 95.8 95.6 0.09 95.5 97.4 96.6

As is clear from these Figures and Tables, also in the three-elementsystem, it is possible to control the relative permittivity εr throughadjustment of the Mg₂SiO₄ content and control the temperaturecoefficient τf through adjustment of the CaTiO₃ content. In thecomposition of 0.2275MgTiO₃-0.6825Mg₂SiO₄-0.09CaTiO₃ prepared with theaim that the relative permittivity εr=10 and that the temperaturecoefficient τf=0, it was found that the relative permittivity εr=10.86and that the temperature coefficient τf=−2.7 ppm/K.

In addition, upon considering the relative density of each sampleproduced, it was found from FIGS. 13 and 16 and Tables 9 and 12 thatgood results could be obtained when the calcining temperature was 1300°C. or more.

As is clear from the foregoing description, according to the presentinvention, the relative permittivity εr and temperature coefficient τfcan be controlled to enable provision of a dielectric porcelaincomposition with the relative permittivity εr suitable forsubmillimeter-wave and millimeter-wave regions and the temperatuecoefficient τf controlled to a value in the vicinity of 0.

Also according to the present invention, using the dielectric porcelaincomposition as a dielectric material enables provision of a dielectricresonator usable in the submillimeter-wave and millimeter-wave bandwidthregions. In the dielectric resonator, since the dielectric porcelaincomposition exhibits appropriate relative permittivity εr, thedimensional tolerance can be alleviated to make it easy to design adielectric resonator when being fabricated. Furthermore, the temperaturecoefficient can also be controlled in compliance with the temperaturecoefficient of the surrounding parts and the like.

The present disclosure relates to subject matter contained in JapanesePatent Application Nos. 2003-071545, filed on Mar. 17, 2003, thecontents of which are herein expressly incorporated by reference in itsentirety.

1. A dielectric porcelain composition calcined at a temperature of not less than 1300° C. comprising MgTiO₃, Mg₂SiO₄ and CaTiO₃ and satisfying a+b+c=1, 0<b<1 and 0<c≦0.15, wherein a denotes a molar ratio of MgTiO₃, b denotes a molar ratio of Mg₂SiO₄ and c denotes a molar ratio of CaTiO₃.
 2. The composition according to claim 1, wherein the molar ratio b is defined as 0.5≦b<1 and the molar ratio c is defined as 0.05≦c≦0.09.
 3. A dielectric resonator comprising as a dielectric material a dielectric porcelain composition calcined at a temperature of not less than 1300° C. that comprises MgTiO₃, Mg₂SiO₄ and CaTiO₃ and satisfies a+b+c=1,0≦b≦1 and 0<c≦0.15, wherein a denotes a molar ratio of MgTiO₃, b denotes a molar ratio of Mg₂SiO₄ and c denotes a molar ratio of CaTiO₃.
 4. A manufacturing process for a dielectric porcelain composition that comprises MgTiO₃, Mg₂SiO₄ and CaTiO₃, comprising adjusting respective contents of Mg₂SiO₄ and CaTiO₃ to satisfy a+b+c=1, 0<b<1 and 0<c≦0.15, wherein a denotes a molar ratio of MgTiO₃, b denotes a molar ratio of Mg₂SiO₄ and c denotes a molar ratio of CaTiO₃, thereby adjusting relative permittivity εr and temperature coefficient τf, and calcining these materials at a temperature of not less than 1300° C.
 5. A dielectric porcelain composition consisting of MgTiO₃, Mg₂SiO₄ and CaTiO₃ and satisfying a+b+c=1, 0<b<1 and 0<c≦0.15, wherein a denotes a molar ratio of MgTiO₃, b denotes a molar ratio of Mg₂SiO₄ and c denotes a molar ratio of CaTiO₃.
 6. The composition according to claim 5, wherein the molar ratio b is defined as 0.5 b<1 and the molar ratio c is defined as 0.05≦c≦0.09.
 7. A dielectric resonator comprising as a dielectric material a dielectric porcelain composition consisting of MgTiO₃, Mg₂SiO₄ and CaTiO₃ and satisfies a+b+c=1, 0<b≦1 and 0<c≦0.15, wherein a denotes a molar ratio of MgTiO₃, b denotes a molar ratio of Mg₂SiO₄ and c denotes a molar ratio of CaTiO₃.
 8. A manufacturing process for a dielectric porcelain composition consisting of MgTiO₃, Mg₂SiO₄ and CaTiO₃, comprising adjusting respective contents of Mg₂SiO₄ and CaTiO₃ to satisfy a+b+c=1, 0<b<1 and 0<c≦0.15, wherein a denotes a molar ratio of MgTiO₃, b denotes a molar ratio of Mg₂SiO₄ and c denotes a molar ratio of CaTiO₃, thereby adjusting relative permittivity εr and temperature coefficient τf. 